As is known, a tire of the type considered has beads designed to co-operate with the seats of a mounting rim, the beads being connected to a tire crown by sidewalls. The tire comprises a carcass reinforcement formed of at least a plurality of metallic or non-metallic cords orientated in a meridian direction, i.e. a direction that makes an angle equal or close to 90° with the circumferential direction. This carcass reinforcement is anchored in each bead to at least one circumferential bead reinforcement (for example a bead wire), forming an upturn. The carcass reinforcement is surmounted radially by a crown reinforcement consisting of at least two stacks of metallic reinforcement elements crossed over from one stack to the next, which form angles between 10° and 45° with the circumferential direction. In addition, the upturns of the carcass reinforcement are usually reinforced by at least one supplementary reinforcement whose reinforcing elements, whether metallic or not, are arranged so as to make an angle smaller than 45° with the circumferential direction.
Under certain types of stressing the tire beads are subjected to conditions of relatively high temperature compared with the average working temperatures. These temperature increases arise mainly because of heating of the brake components of heavy vehicles and the radiation that results from this.
To increase the endurance of the tire beads it is known to provide said beads with supplementary reinforcements arranged in the beads so that they are interposed between the seat of said beads and the circumferential reinforcement anchoring the carcass reinforcement. However, this solution causes high stresses to appear at the radially outer end of said supplementary reinforcements, and these stresses can adversely affect the endurance of the tire.
In another solution (described in particular in patent publication FR 1328752) a bead is described which comprises a bead wire around which is wrapped the carcass reinforcement and its upturn. Although this solution effectively improves the endurance of the bead, it is nonetheless not totally satisfactory, in particular because it entails positioning a wrapping of cords on the radially outer portion of the bead wire and upturn so as to hold said upturn firmly onto the bead wire.
Granted that the useful life of tires is increasing (in particular when judged using the criterion of tread wear), it has been found that high temperatures repeatedly applied to the tire lead to permanent deformations of the beads which reduce the endurance of said beads.
The aim of the present invention is to obtain a tire bead structure for vehicles carrying heavy loads, this structure conferring upon said bead an endurance appropriate in relation to the user's needs while reducing the number of components.